Method of uniting metals



Patented Apr. 10,

METHOD OF UNITING METALS Raymond B. Hobrock, Troy Township, OaklandCounty, Mich, assignor to Bondy Tubing Company, Detroit, Mich., acorporation of Michigan No Drawing. Application July 17, 1944, SerialNo. 545,413

1 Claim.

This invention relates to a method of uniting or bonding togetherseparate bodies of metal or two portions of the same body of metal bymeans of another metal employed as a uniting or bonding metal andwherein the metal of one or both of the two bodies and the uniting orbonding metal rapidly alloy with each other; especially when subjectedto heat.

This application is a continuation in part of application Serial No.417,405, flied October 31, 1941, which is itself a continuation in partof application Serial No. 391,595, filed May 2, 1941.

A diflicult problem is presented in the making -of a joint between'metal bodies or uniting or bonding the metal bodies where the metalused as the bonding medium very readily and rapidly alloys with themetal of one or both of the bodies. On the other hand, the employment ofmetals having such rapidly alloying characteristics is often desirableand often necessary to the production of a desired article. For example,metals having corrosion resisting characteristics should be used whereresistance .to corrosion is a necessary characteristic in the finishedarticle and yet the corrosion resisting metals of the desired type maynot be usable as they cannot be satisfactorily bonded together or unitedby the methods heretofore known. Requirements other than resistance tocorrosion may dictate the use of various metals.

A number of metal combinations fall within the classificationcontemplated herein. The term metal combinationflis used with referenceto the metal. in one or more or the bodies which are to be united andthe metal used as the bonding medium. In these metal combinations thebody metal is the one with the higher melting temperature and thebonding metal is the one with the lower meltingtemperature. Among themetal combinations are these: body metal of a copper-nickel alloy, suchas Monel metal, and a bonding metal of copper; body metal of nickel andbonding metalof copper; body metal of silver and bonding metal of lead;body metal of platinum and bonding metal of gold; body metal oi'copperand bonding metal of bismuth: body metal or gold and bonding metal ofsilver; body metal or nickel and bonding metal of gold.

Alloys of the above metal combinations may be united by the methodherein described where the alloys are such that the combination ofmetals prcsent'theproblem oi the rapid alloying at temperatures abovethe melting temperatures)! thebondingmetsl. In allimtance the bodycomprised of the metal in the combination may be united to a body ofanother metal.

In accordance with the invention the surface of at least one of thebodies is provided with a coating of the bonding metal. The two bodiesare then' placed together in interfacial relationship with the coatinglying between the bodies and constituting one of the interfaces. Wherethe metal of the coating and the metal of at least one of the bodiesreadily and rapidly alloy with each other, the metal of the coating maybe completely absorbed and alloyed into the metal of the body while in asolid state, particularly when subjected to heat. In such a case, thereis a complete failure to establish a bond. Once the coating metal isrendered molten, the alloying of the coating and metal of the body orbodies alloy together with increased rapidity.

The situation is a dynamic one in that once the coating metal isrendered molten there is a rapid alloying of the coating metal and thebody metal resulting in an ever increasing melting point of the alloy soformed and requiring an increase in temperature to maintain a moltenstate. The bonding metal employed should have a melting point lower thanthat of the bodies to be united. If the temperature is not increasedafter the bonding metal becomes molten the alloying of the bonding metalwith the body metal results in the formation of an alloy which freezesas its melting p'oint'reaches or exceeds the existing temperature. Thisprevents the proper flowing or migration of the bonding metal and anincomplete bonding process and the failure to unite the interfaces ofthe bodies or portions thereof.

Thus, it may be said that the average rate of in- V crease in thetemperature is greater than the average rate of elevation of thefreezing point of the alloy which is being formed by the alloying of thebonding metal and the metal of one or both of the bodies. The rate doesnot have to be uniform throughout the range so long as the temperatureis maintained above the freezing point of the forming alloy. Also, theinvention contemplates and provides a method wherein the temperature isincreased with such rapidity,

throughout the temperature range below the melting point of the bondingmetal, as to prevent complete alloying of the bonding metal with thebody metal in a solid state. To these ends, it is preferable that themetals be heated by generation of heat within the metals asdistinguished from the heating of the metals by radiation, althoughfurnaces may be developed, such as the radiant tube furnace, which willprovide a sumcient temperature gradient to effect heat transfer to themetals in a manner suiilcient for the purpose. The work is preferablyheated by the electrical resistance method or the electrical inductancemethod.

An example of the invention. may be given with reference to thecombination of the metal known as Monel and copper, wherein at least oneof the bodies comprises Monel metal andthe bonding medium comprisescopper. .As is well known, Monel is a metal having about 67% to 70% ofnickel and the remainder of copper, except for impurities which mayinclude a small percentage of iron. Monel metal has a number offavorable characteristics which are better than characteristics of othercopper-nickel alloys. such as high yield strength, ultimate strength,working ability, corrosion resisting characteristics, etc. If thesecharacteristics are to he maintained, then the bond or Joint should havecopper-nickel per-- centages proximating those of the Monel metal.

In this example, a thin coating of copper was applied to the surface ofthe bodies although the copper may be applied to the surface of but onebody. By the employment of a small amount of copper the Monel metal isnot made overly rich with copper and the provision of a homogeneousstructure is facilitated. The amount of copper coated on the bodysurface was within the range of about .15 to .5 ounce for two squarefeet of surface. The copper was and is preferably applied byelectro-deposition. The surfaces were then placed in-interfacialrelationship with the copper coating constituting one or bothinterfaces. The metals; or work, as the metals may be called, were nowheated. This was accomplished by electrical induction, and in othercases, by electrical resistance. The temperature of the work was raisedfrom roomtemperature to copper melting temperature in about one-half asecond. This substantially prevents the alloying of the copper and thenickel in the Monel body while the copper is in a solid state. After themelting temperature of copper was attained the molten condition wasmaintained for about two seconds, and then the raising of thetemperature was discontinued to cause solidification.

As soon as the copper becomes molten, however, the rate of the alloyingof the copper and the nickel in-the Monel metal increases rapidly and,as the resultant alloy becomes enriched in nickel its freezing pointraises and there would be a solidification except for an important stepin the process. This step resides in the heating or the bodies to raisethe temperature thereof to a temperature between the melting temperatureof the copper and the melting temperature of either body at an averagerate of temperature increase in the range from the melting temperatureof the copper to the maximum temperature attained, which is greater thanthe rate of elevation of the freezing point of the alloy formed by thealloying of the copper and the Monel metal. Thus, the alloying metals atthe interfaces are maintained in a molten state during the time ofrising temperature and then the raising of soft or mushy is about 1315C. whereas the copper melting temperature is 1084 C. It will be seen,therefore, that it is essential not to subject the work to a temperaturethat would melt the bodies and yet the temperature to which thework issubjected must be considerably higher than copper melting temperaturedue to the dynamic nature of the situation. In this example, it ispreferable to heat the work to a point safely below 1315 C., or sayabout 1300 C. However, it has been found that a satisfactory bond can bemade where the temperature is in the vicinity of 1225 C. With thisarrangement the copper and the Monel are so alloyed with each other,that according to the best available tests which can be made at present,the copper-nickel proportion at the bond or joint are within about 2% ofthat of the original Monel metal. The resultant article is, as a result,substantially seamless as there is a substantially homogeneous structurethroughout the united bodies and across the bond or joint. The termcopper" used herein with reference to the bonding or sealing metal is tobe construed to cover commercial copper or cuprous metal or brazingbrasses or bronzes.

The metals of the other combinations are treated in the same manner asthe copper-nickel alloy and copper combination is treated, with dueregard, however, to the differences in'melting temperatures. The nickeland copper combination may be satisfactorily handled to unite the nickelbody to another body by employing the same temperatures and timing givenin the above example for the copper-nickel alloy and copper combination.The lead melts at a relatively low temperature, namely, 621 F. relativeto the silver which has a melting point of l76l F. so that there isquite a large temperature range in this combination. In the platinum andgold combination there is also a substantial range of temperature fromthe melting temperature of gold which is 1945 F. to that of platinumwhich is 3224 F. A large temperature range is also present in the copperand bismuth combination since bismuth melts at 520 F., as against copperwhich melts at 1981 F. The range lessens in the nickel and goldcombination, lying between the melting temperature of gold, namely, 1945F. and the melting temperature of nickel 2650 F. A relatively smallrange occurs in the gold and silver combination, namely, between 1761"F. and 1945 F. In treating any of these combinations, the rate oftemperature increase, above the melting temperature of the bondingmetal, exceeds the rate of elevation of the freezing point of theforming alloy, so as to maintain a molten state up to the point of themaximum temperature attained, which necessarily, is sufficiently belowthe melting temperature of the metal body in question so as not to meltthe body or the alloy thereof.

I claim:

The method of uniting two metal bodies by the employment of a. bondingmetal wherein, at least one of the metal bodies is selected from thegroup consisting of silver, platinum, copper.

gold, and nickel and wherein the bonding metal is selected respectivelyfrom the group consisting of lead, gold. bismuth, silver and gold, and,

comprises placing a coating of the bonding metal on a surface of atleast one of the bodies, disposing the bodies, while in a solid state,in interiacial relationship with the coating of bonding metalconstituting one of the interracial surfaces, heating the bodies toraise the temperature thereof to a temperature between the meltingtemperature of the bonding metal and the melting temperature of eitherbody at an average rate of temperature increase, in the range from themelting temperature of the bonding metal to the maximum temperatureattained, which is greater than the rate oi elevation oi the freezingpoint of the alloy formed adjacent the interfaces by the alloying of thebonding metal and the metal of said first mentioned one body, whereby tomaintain the alloying metals ad- Jacent the interfaces in a molten state'during the time of rising temperature and then discontinuing theraising of the temperature of the bodies to cause solidification of thealloyed metals with all of the bonding metal alloyed with the metalbodies.

RAYMOND H. HOBROCK.

